THE 1201 SUPERCONDUCTORS HG1-Y(VO4)(Y)(BA,SR)(2)CUO4-2Y- EVIDENCE FORVO4 TETRAHEDRA(DELTA )

A series of mercury based cuprates with nominal composition Hg1-yVyBa2 -xSrxCuO4+2y+delta has been prepared for x = 0, 0.25, 0.5, 0.75, 1 and 1.25. The actual solid solution limit from the EDS measurement is x 1 .1, y ranges from 0.2 to 0.35. The single crystal study coupled with h igh resolution electron microscopy shows for the first time the presen ce of VO4 tetrahedra replacing partly the mercury atoms according to t he formulation Hg1-y(VO4)(y)(Ba,Sr)(2)CuO4-2y+delta. The role of vanad ium for the stabilisation of the structure and as a doping agent in th e superconducting properties is discussed. (C) 1997 Elsevier Science B .V.